Datasheet
LPC11U6x All information provided in this document is subject to legal disclaimers. © NXP Semiconductors N.V. 2014. All rights reserved.
Product data sheet Rev. 1.2 — 26 May 2014 77 of 96
NXP Semiconductors
LPC11U6x
32-bit ARM Cortex-M0+ microcontroller
Remark: When a self-powered circuit is used without connecting VBUS, configure the
PIO0_3/USB_VBUS pin for GPIO (PIO0_3) and provide software that can detect the host
presence through some other mechanism before enabling USB_CONNECT and the
SoftConnect feature. Enabling the SoftConnect without host presence leads to USB
compliance failure.
14.3.1 USB Low-speed operation
The USB device controller can be used in low-speed mode supporting 1.5 Mbit/s data
exchange with a USB host controller.
Remark: To operate in low-speed mode, change the board connections as follows:
1. Connect USB_DP to the D- pin of the connector.
2. Connect USB_DM to the D+ pin of the connector.
Use the IRC as clock source for the USB PLL to generate 48 MHz, then set the USB clock
divider USBCLKDIV to 8 for a 6 MHz USB clock (see Figure 10 “
Clock generation”).
External 10 resistors are recommended in low-speed mode to reduce over-shoots and
accommodate for 5 m cable length required for USB-IF testing.
Two options exist for connecting VBUS to the USB_VBUS pin:
(1) Connect the regulator output to USB_VBUS. In this case, the USB_VBUS signal is HIGH whenever the part is powered.
(2) Connect the VBUS signal directly from the connector to the USB_VBUS pin. In this case, 5 V are applied to the USB_VBUS pin
while the regulator is ramping up to supply V
DD
. Since the PIO0_3/USB_VBUS pin is only 5 V tolerant when V
DD
is at operating
level, this connection can degrade the performance of the part over its lifetime. Simulation shows that lifetime is reduced to
15 years at T
amb
= 45 °C and 8 years at T
amb
= 55 °C assuming that USB_VBUS = 5 V is applied continuously while V
DD
= 0 V.
Fig 39. USB interface on a bus-powered device
REGULATOR
VBUS
LPC1xxx
V
DD
R1
1.5 kΩ
aaa-010821
USB-B
connector
USB_DP
USB_DM
V
SS
R
S
= 33 Ω
R
S
= 33 Ω
USB_VBUS
(2)
USB_VBUS
(1)
USB
USB_CONNECT
D+
D-